1. Field of Invention
This invention relates to a harvesting header for a combine harvester, and more particularly, to a header frame having a diagonal truss member with a length adjustment mechanism used to change the amount of bow in the header frame.
2. Description of Related Art
Agricultural harvesters such as combines are typically equipped with a harvesting header. For example, corn headers are specifically designed to pick corn and vary in size from two-row units to twelve-row units or more. As the harvester moves through the field, each row-unit passes between rows of corn. Corn header row units typically use gathering chains to covey crop material and ears rearward toward a cross auger. A set of driven snap rolls, which rotate based on the speed of the harvester, grabs the corn stalks and forces them downward between stripper plates. The ears of corn are snapped free of the stalk and the cross auger passes the ears to the feeder housing of the harvester. If the snap rolls are operated too fast or too slow, ears of corn may be lost or entire corn stalks may be passed to the cross auger and feeder housing.
Over the years, the width of harvesting headers has increased in order to reducing the number of passes through the field required by the harvesting machine to cover the entire field. However, as the width of headers increases, the amount of flexing of the structure of the header which occurs has also increased. This has resulted in increased difficulties in maintaining the header in a straight orientation for proper operation. Headers are typically supported by the harvesting machine at a location in the middle of the header. When the header is suspended above the ground, the ends of the header tend to deflect downward under the load. As headers increase in width, it is harder to prevent this deflection.
Header manufacturers have taken various approaches to address this problem. One approach is to build a header frame with an inner section having a pair of central inner support beams spaced outwardly from a midpoint of the header and a pair of outer sections having at least one outer pair of support beams which are arranged at or adjacent the outer ends of the inner section. A number of braces and gussets connect to the beams to form a truss like structure to reduce the deflection. The individual pieces are welded together with the intent that the header will resist deflection under load. However, stresses can concentrate at the interfaces between the sections leading to frame failure or requiring additional reinforcement.
In order to accommodate this downward flexing of the outer ends of the header, in initial manufacture, the support beams of the header are welded such that, in an unstressed condition, the header is upwardly concave, that is the middle portion of the header is lower than the outer end of the header. When the header is fully assembled onto the harvesting combine, the weight of the header tends to flex the frame so as to reduce the concave shape. However, the weight and positioning of header components during assembly can vary so it is not always possible to properly calculate the required concave shape. Additionally, over time, the frame may continue to settle into an upwardly convex shape in which the ends are lower than the center.